Simplex Noise

package net.buddat.dynamic.map.gen;

import java.util.Random;

public class SimplexNoise {

    private static int grad3[][] = { {1,1,0},{-1,1,0},{1,-1,0},{-1,-1,0},
                                    {1,0,1},{-1,0,1},{1,0,-1},{-1,0,-1},
                                    {0,1,1},{0,-1,1},{0,1,-1},{0,-1,-1}};

    private static int p[] = { 151,160,137,91,90,15,
                            131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
                            190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
                            88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
                            77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
                            102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
                            135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
                            5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
                            223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
                            129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
                            251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
                            49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
                            138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180};

    // To remove the need for index wrapping, double the permutation table length
    private static int perm[] = new int[512];
    static {
        for(int i = 0; i < 512; i++)
            perm[i] = p[i & 255];
    }

    // This method is a *lot* faster than using (int)Math.floor(x)
    private static int fastfloor(double x) {
        return x > 0 ? (int)x : (int)x - 1;
    }

    private static double dot(int g[], double x, double y) {
        return g[0] * x + g[1] * y;
    }

    // 2D simplex noise
    public static double noise(double xin, double yin) {
        double n0, n1, n2;

        final double F2 = 0.5 * (Math.sqrt(3.0) - 1.0);
        double s = (xin + yin) * F2;
        int i = fastfloor(xin + s);
        int j = fastfloor(yin + s);

        final double G2 = (3.0 - Math.sqrt(3.0)) / 6.0;
        double t = (i + j) * G2;
        double X0 = i - t;
        double Y0 = j - t;
        double x0 = xin - X0;
        double y0 = yin - Y0;

        int i1, j1;
        if (x0 > y0) {
            i1=1;
            j1=0;
        } else {
            i1 = 0;
            j1 = 1;
        }

        double x1 = x0 - i1 + G2;
        double y1 = y0 - j1 + G2;
        double x2 = x0 - 1.0 + 2.0 * G2;
        double y2 = y0 - 1.0 + 2.0 * G2;

        int ii = i & 255;
        int jj = j & 255;
        int gi0 = perm[ii + perm[jj]] % 12;
        int gi1 = perm[ii + i1 + perm[jj + j1]] % 12;
        int gi2 = perm[ii + 1 + perm[jj + 1]] % 12;

        double t0 = 0.5 - x0 * x0 - y0 * y0;
        if(t0 < 0)
            n0 = 0.0;
        else {
            t0 *= t0;
            n0 = t0 * t0 * dot(grad3[gi0], x0, y0);
        }

        double t1 = 0.5 - x1 * x1 - y1 * y1;
        if(t1 < 0)
            n1 = 0.0;
        else {
            t1 *= t1;
            n1 = t1 * t1 * dot(grad3[gi1], x1, y1);
        }

        double t2 = 0.5 - x2 * x2 - y2 * y2;
        if(t2 < 0)
            n2 = 0.0;
        else {
            t2 *= t2;
            n2 = t2 * t2 * dot(grad3[gi2], x2, y2);
        }

        return 70.0 * (n0 + n1 + n2);
    }

    public static void genGrad(long seed) {
        Random rnd = new Random(seed);
        for(int i = 0; i < 255; i++)
          p[i] = i;
        for(int i = 0; i < 255; i++) {
          int j = rnd.nextInt(255);
          int nSwap = p[i];
          p[i]  = p[j];
          p[j]  = nSwap;
        }

        for(int i = 0; i < 512; i++)
            perm[i] = p[i & 255];
    }

}